Public bug reported:
This is actually a duplicate to
https://bugzilla.kernel.org/show_bug.cgi?id=203183 that is for internal
tracking.
[Overview]
On Intel CoffeeLake it's observed tsc is always marked unstable after
turning off screen and let cpu enter idle state Package C10(PC10), and
then clock source is switched to hpet. Following messages are printed in
dmesg when this occurs:
[ 115.454117] clocksource: timekeeping watchdog on CPU2: Marking clocksource
'tsc' as unstable because the skew is too large:
[ 115.454146] clocksource: 'hpet' wd_now: a44e6960 wd_last: a42fe23b mask:
ffffffff
[ 115.454151] clocksource: 'tsc' cs_now: 69ee1f8d9f cs_last: 699580f6fd mask:
ffffffffffffffff
[ 115.454160] tsc: Marking TSC unstable due to clocksource watchdog
[ 115.454675] TSC found unstable after boot, most likely due to broken BIOS.
Use 'tsc=unstable'.
[ 115.454679] sched_clock: Marking unstable (115712298090,
-257671127)<-(115460381128, -5706726)
[ 115.455825] clocksource: Switched to clocksource hpet
[Step to reproduce]
1. use `powertop` to observe if CPU has ever enter PC10,
2. issue `xset dpms force off` to turn off screen and idle for some minutes,
3. check dmesg for above tsc marked unstable messages
[Actual Results]
TSC marked unstable and clock source switched to HPET.
[Expected Results]
TSC remains the clock source across the PC10 event.
[Build Date & Hardware]
This is reproducible on kernel version 4.14 through 5.1-rc2. Order
kernel versions are not tested.
[Additional Information]
This was first found on Ubuntu (all versions) that system doesn't go
suspend after stayed idle for 20 minutes. Clock source was switched to
HPET, the system time is no correctly synced with reality so that the
system doesn't consider it has stayed idle long enough to begin suspend
process.
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Tags: tsc-unstable
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https://bugs.launchpad.net/bugs/1840239
Title:
tsc marked unstable after entered PC10 on Intel CoffeeLake
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